Veneer defect detector and clipper control

ABSTRACT

Method of providing actuating signals to a cutting device having assymetrical actuation response characteristics in such a way that material is cut precisely at preselected locations includes manual or electronic means for generating cutting command signals, either as a result of a defect in the material or after predetermined lengths of material have moved through the cutting device, and means for introducing a time delay between the cutting command signals and those signals which actuate the cutting device. The magnitude of the time delay is determined by the speed at which the material moves through the cutting device and by the response characteristics of the cutting device to the actuating signals. If no defects are found in the material, the material will be cut automatically into predetermined standard lengths.

United States Patent 1 1 3,760,667 Maxey et al. Sept. 25, 1973 [54] VENEER DEFECT DETECTOR AND 2,978,943 4/1961 Baliut 83/362 CLIPPER CONTROL 3,165,961 1/1965 Hammond 83/365 Assignee:

Filed:

Inventors: Carl W. Maxey; Grant R. Montague;

Warren L. Leyde; Eugene L. Bryan, all of Arcata, Wash.

The Dlack Claws0n Company,

Hamilton, Ohio Aug. 3, 1972 Appl. No.: 277,791

Related US. Application Data Continuation of Ser.'No. 78,082, Oct. 5, 1970,

abandoned, Division of Ser. No. 800,324, Jan. 15, 1969, Pat, No. 3,552,252, which is a continuation of Ser. No. 552,940, May 25, 1966, abandoned.

US. Cl 83/13, 83/42, 83/362,

int. Cl B26d 5/38 Field of Search 83/13, 362, 363, 83/76, 74, 365, 42, 522, 371; 340/190, 259

References Cited UNlTED STATES PATENTS GREEN Hervey 83/522 X Primary ExaminerFrank T. Yost Att0rney--Marechal, Biebel, French & Bugg [5 7 ABSTRACT Method of providing actuating signals to a cutting device having assymetrical actuation response characteristics in such a way that material is cut precisely at preselected locations includes manual or electronic means for generating cutting command signals, either as a result of a defect in the material or after predetermined lengths of material have moved through the cutting device, and means for introducing atime delay between the cutting command signals and those signals which actuate the cutting device. The magnitude of the time delay is determined by the speed at which the material moves through the cutting device and by the response characteristics of the cutting device to the actuating signals. If no defects are found in the material, the material will be cut automatically into predetermined standard lengths.

4 Claims, 16 Drawing Figures CLIPPER coiasou-z CL'lP I. mi l 22 ELAY INSERTION D DELAY SERVO PAlfNlfinserzsma 1 760.66

mm 02 or 11 L T. V R R N 5 u L EU lg}: C mw .5 JR LA TAI. DI E AC CB H 4 o .l P 6 T C CHANNEL-l INDIVIDUAL PHOTOCELL VENEER DEFECT DETECTOR AND CLIPPER CONTROL Related Applications This application is a continuation of US. Pat. application Ser. No. 78,082, filed Oct. 5, 1970, and now abandoned which is a division of US. Pat. application Ser. No. 800,324, filed Jan. 15, 1969 (now US. Pat. No. 3,552,252, issued Jan. 5, 1971), which is a continuation of US. Pat. application Ser. No. 552,940, filed May 25, 1966, now abandoned.

VENEER DEFECT DETECTOR AND CLIPPER CONTROL This invention relates to a clipper control for use in cutting moving sheet material such as a wood veneer ribbon and to a detector apparatus and to a novel method to aid in the removal of defective areas from rapidly moving sheet material.

It is presently the practice of the veneer industry for an operator to scan visually moving ribbons of veneer to determine the occurrence and location of a defect. The operator estimates the rate of veneer travel, estimates the time required for the defect to travel into a veneer clipper and then actuates the clipper control switch at the proper moment to cut the veneer as close to the defect as possible thereby to eliminate completely the defect without cutting away acceptable veneer.

The operator must be experienced and possess considerable skill and judgement in order to anticipate when the clipper knife will actually contact and cut the veneer ribbon since the response time of the clipper, i.e., the time between the closing of the clipper control switch and the actual engagement of the knife with the veneer, may vary to a considerable degree with changes in the operating temperature or changes in the means supplying the power to the clipper.

In addition, clippers having a toggle actuated knife have a different response time when the toggle is moving to the rightand' when the toggle is moving to the left. The operator must compensate for this asymmetrical nature of the clipper and accurately anticipate the delay in the response time if the veneer is to be cut as close to the defect as possible and not leave an excessive amount of good veneer in the removed portion, or leave a portion of the defect in that part of the veneer which is considered acceptable.

In one of the toggle actuated veneer clippers in common use, a source of air pressure is supplied through an electrically actuated pneumatic control valve to air cylinders to cause the clipper toggle bar to move in one of two directions. A variation in the response time of this pneumatic control valve to the actuating signal will introduce a variation in the operation of theknife and thereby cause inaccurate cutting of the veneer. It is not uncommon for electrically actuated pneumatic solenoids, if operated on alternating currents, to vary in their response time by as much as one one hundred twentieth of a second. This variation in the time of the response may cause an error of as great as one-fourth inch in the actual cutting of a veneer ribbon traveling at a rate of 150 feet per minute. Attempts have been made to use direct current controls to eliminate this source of error, but even these controls are subject to long term drift and will ultimately allow a variation in the response rate of the clipper.

It is also the practice of the industry to utilize the same type of clippers described above to cut the veneer into standard lengths if no defects are present. Two methods are in common use to provide measurement for the cutting of standard lengths of veneer. One method uses a photocell limit switch arrangement which senses the leading edge of the veneer after it has been cut. The photocell method is restricted in its use by the fact that the measurement is accurate only on perfectly flat pieces and if the flow rate of the veneer is accurately known. Another method uses a cam follower wheel which travels with the veneer to indicate when a length of veneer has passed beneath a clipper without a defect. The cam follower must follow the veneer precisely in order to measure the length of the veneer accurately, but vibration and sudden changes in ribbon speed, such as caused by clipping, can cause tracking errors. When used in combination with a device to remove defective regions, the mechanical standard length measuring cam must also be reset each time-a defect is removed so that the standard length thereafter may be measured. It is apparent that the response characteristics of the clipper must also be taken into consideration when performing the standard length clipping function.

Since the standard lengths of veneer must be greater than a certain minimum dimension, but may not be smaller than the minimum dimension, it has been a common practice to determine the total variations introduced by the various components and adjust the equipment such that, using the minimum tolerance in each case, the sheet will not be less than the minimum standard length. The cut veneer sheets from the clipper may vary in size from the required standard length to pieces which may be as much as 1% inch oversize. These oversize sheets which may be ten feet in width, of course, represent a waste which may be considerably reduced if the range of tolerances in the equipment could be reduced.

The present invention eliminates the above mentioned sources of error by providing anelectronic system which aids the operator in determining where a cut is to be made in the veneer and which provides compensating means to adjust automatically the time delay between defect detection and the application of the electrical cutting signal to the clipper such that the clipper knife actually engages the ribbon of veneer at precisely the proper position on the veneer, notwithstanding variations in flow rate of the veneer or drift in the response time of the clipper.

In the present invention, a defect in the veneer may be observed before the veneer enters the clipper, either by the operator as a defect passes a reference location,

or by directing a source of radiation through the veneer sheet and detecting the change in the radiation inten-- sity as an indication of the presence of a defect. Once a defect is detected, an electrical signal is created which is placed into a memory or delay circuit for use in causing the clipper to cut the sheet after the veneer has moved the distance from the reference location on the detector to the clipper. A variable time delay is provided to compensate for variations in the response time of the clipper such that the knife actually cuts the veneer at the exact location preselected by the operator or by the radiation detector.

The effects of the variations in the response time of the clipper due to temperature, air pressure, wear, etc.,

and to the asymmetrical response time characteristics of the toggle type clipper mechanisms commonly in use, may be eliminated by comparing the actual occurrence of the cutting of the veneer to the location where the cutting should occur, and modifying the time of application of the clipper actuating signal to cause the veneer to be cut at the required location. Since the toggle type clipper has two primary response times, two delay circuits are used in conjunction with an electronic memory and these delay circuits are selected in synchronism with the toggle type action of the clipper.

The time delay between sensing the defect at the reference location and the actual occurrence of the clipping operation will vary depending upon the velocity of the veneer. Since various velocities or veneer flow rates can be accommodated, the electronic memory providing the necessary delay is made flexible to insure that the knife cuts the veneer at the exact location previously selected. A tachometer is placed in mechanical contact with the flowing sheet of veneer and produces a series of pulses, each pulse corresponding to a inch increment of veneer travel. The electronic memory providing the delay is divided into two parts, the first providing a delay which is dependent solely upon the distance the veneer travels irrespective of the veneer velocity, and the second being related to the velocity of the veneer. The electronic memory is divided between the two types of delay means to provide for flexibility and accuracy in the operation of the system.

Two methods are employed in a preferred embodiment of this invention in locating defects in moving veneer sheets, one of which includes using a visual reference means to permit the operator to actuate a switch manually when a defect passes the reference location, and the other means includes using a photoelectric system measuring the intensity of the radiation transmitted through the veneer to indicate the presence of defective wood.

The manual method uses a shadow line produced on the veneer by a source of radiation situated above the traveling sheet and a wire stretched perpendicularly to the veneer travel and between the source and the veneer. When using the shadow line reference in conjunction with the time delay means which compensates for the drift and asymmetrical characteristics of the toggle type clipper, more accurate cutting of the wood is possible with a resultant savings in money since less waste is created. By providing a shadow line reference, the operator no longer must watch a defect approach the clipper and anticipate when the blade will cut the veneer. Therefore, the operators reflexes and judgment are no longer major factors in determining the location of the cut.

The photoelectric type of defect detector includes a plurality of photoelectric cells positioned beneath the traveling veneer which are primarily sensitive to the infrared radiation which passes through the veneer. When a defect occurs, such as a knot, or a void in the veneer, the photocells will receive an additional amount of radiation and will actuate appropriate circuitry to cause the defect to be removed.

It has been found that sound veneer absorbs more radiation than large knots or voids in the wood. This is due to the microscopic anatomy of the wood where it appears that the wood itself is formed from an aggregate of tubular shaped units or cells with their longer axis aligned with the longitudinal axis of thetree memher. Thus, the cells are aligned vertically in the tree trunk, and horizontally in the limbs of the tree. Since the veneer is removed from the tree in such a way that the thickness dimension of the veneer is almost perfectly radial with respect to the longitudinal axis of the tree, all of the cells which comprise the wood will be in the same plane and will be parallel to the supporting table. As the veneer continues to be stripped from the tree, the limbs will be sliced at right angles producing knots. The cell orientation of the knots will. be perpendicular to that of good wood and will be aligned parallel to the thickness direction. The infrared radiation will therefore pass through the material more readily when a knot is present due to this cell orientation. The photoelectric transducer therefore measures the intensity of the radiation and indicates the presence of a defect when the radiation received increases.

Since the area immediately adjacent to a defect which is observed by the photocells is also disclored and may be considered defective or unacceptable, it is often desirable to remove a portion of the wood which immediately precedes and that which follows the defective area as observed by the photoelectric detector. A circuit is provided in the present invention within the time delay memory to cause the knife to cut the veneer a first predetermined distance before the area of the defect (lead) and to cut the veneer at a second predetermined distance after the defect passes beneath the knife (lag). Both the lead and lag distances may be equal.

The photoelectric cells are divided into regions which extend transversely across the ribbon of veneer. When the operator observes the defect approaching the detectors, he activates the photocell region through which the defect will pass to establish a reference level for the radiation which is transmitted through acceptable wood. When the defect thereafter passes through the detecting region, an increase in intensity will be observed. Since wood varies in its infrared transmission characteristics due to changes in thickness, wood type, wood coloring, and other factors, it is desirable to have a detecting device which is flexible and which may accept any type of wood without requiring constant manual readjustment of the detecting device. For this reason, and because the photocell sensitivity and radiation source intensity may also vary, the operator, immediately prior to the observation of a defect, activates the particular cell region through which the defect will move thereby to establish automatically the reference level for the photocells. When the defect leaves the detecting region, a change in intensity is again noted and this change is utilized to cause the clipper again to operate thereby isolating the defective area and completely removing it from the veneer ribbon.

The photocell detector of this invention may also be used to detect the presence of acceptable wood which exceeds a certain predetermined width in what is called the round up fish tail mode. In this mode, much of the wood being stripped from the tree initially is in the form of small broken pieces which cannot be used as veneer, but does contain wood exceeding a predetermined width which may be utilized. Therefore, rather than detecting defects in the veneer, which would be extremely numerous under these conditions, the photocell detectors are connected to a logic circuit which indicates when wood exceeding a predetermined width is present beneath the detector.

The photocell detector is divided into approximately seven regions and in the preferred embodiment of this invention three consecutive photocell regions must indicate the presence of acceptable wood. When wood of the acceptable minimum predetermined width is present, the clipper will separate that portion of the veneer from the remainder of the wood. Should the acceptable region of the wood extend laterally, while maintaining the minimum predetermined width, a different set of three consecutive photocell regions would be activated, and since the initial set of photocell regions no longer indicate the necessary minimum dimensions, another clipping pulse will be initiated. On the other hand, should the initial set of three photocell regions continue to sense acceptable wood, no further clipping pulses would be created even though other photocell regions may begin sensing acceptable wood.

Since the electronic circuitry used in detecting the occurrence of defects or good wood can respond extremely rapidly, and since the mechanical clipper is limited in its response time due to the inertia inherently present in that type of device, a further memory circuit is provided to hold any clip command pulses which occur too frequently to be responded to by the clipper so that a complete removal of a defective area may be accomplished even though the defective area has a dimension less than the response capability of the clipper. The memory merely resupplies the necessary clip pulse after a sufficient time delay has passed, based upon the mechanical limitations of the clipper.

The electronic circuitry included in the present in vention also provides that, in the event no defects occur in the veneer, the wood may be cut into one of two standard lengths, with the longer of the lengths preferred. Therefore, the longer length will be cut from the continuous veneer ribbon unless a defect occurs in the region between the shorter predetermined length and the longer predetermined length, in which case the shorter standard length will be cut and the defect removed. lncreased accuracy in this function is also made available by use of the standard length memory circuits in conjunction with the compensating means for the clipper response.

The photocell detectors are also provided with a logic circuit which detects lateral movement of the veneer and makes insensitive the edge cells which have been exposed on one side of the detector and which activates corresponding detecting cells on the other side of the detector. This arrangement permits the ribbon of veneer to wander laterally without producing a clip pulse merely because one edge photocell became exposed, provided that its corresponding photocell on the other side of the ribbon became covered, but which permits the continuous observation of the edges, of the veneer for defective regions.

Accordingly, it is an object of this invention to provide a clipper control device which automatically com-' pensates for variations in the response time of the clipper due to drift caused by changes in air pressure, temperature, wear, etc., and which compensates for the asymmetrical response characteristic of the clipper and thereby to cause moving sheet material such as veneer to be cut accurately at a location which was preselected prior to the sheet material passing through the clipper.

It is another object of this invention to provide a mechanism whereby moving sheet material may be cut into one of two possible standard lengths with the actual cut being made at the longer of the two standard lengths should no defects occur in the region between the shorter standard length and the longer standard length.

It is another object of this invention to provide a control device for a sheet material clipping mechanism which compensates for variations in the velocity of the sheet material and for variations in the response time characteristics of the clipper mechanism such that the sheet material may be cut within close tolerances at a location preselected either by an operator by a photoelectric detection device, or cut into standard lengths as determined by a length measuring means.

It is another object of this invention to provide a method of detecting defects in moving sheet material wherein a shadow producing device is positioned between a source of visible light and the sheet material to establish a reference shadow line whereby an operator may visually observe a defect passing said shadow line and manually operate an electrical switch to produce a cutting command signal which causes the defect to be removed from the sheet material after the sheet material has moved a predetermined distance.

It is another object of this invention to provide a method for detecting and removing defects from moving sheet material wherein a source of radiation is positioned on one side of the material and a radiation detector is placed on the other side of the material to sense the radiation transmitted therethrough, wherein a reference signal indicating the level of radiation passing through acceptable material is established, wherein a cutting command signal is produced indicating a defect when the intensity of the radiation transmitted through the material increases above a reference level, and wherein the cutting command signal is utilized to cut the material to remove the defect after the material has moved a predetermined distance.

It is another object of this invention to provide a process for detecting and separating acceptable sheet material exceeding a predetermined width from moving sheet material wherein a photoelectric defect detecting element including a plurality of photocells senses the radiation passing through the moving sheet material and establishes when a predetermined number of consecutive photocells indicates the presence of acceptable sheet material to produce a cutting command signal, and thereafter produce additional cutting command signals whenever the width of acceptable sheet material either decreases below said predetermined width or whenever the sheet material of acceptable width does not have at least one edge portion corresponding to the edge of the sheet material initially having the minimum predetermined width.

it is another object of this invention to provide a visual reference means located a predetermined distance from the clipper by which the operator may establish the exact location of a defective area within moving sheet material and manually initiate a cutting singal by reference to the visual reference means, and toprovide a control means to automatically compensate for the variations in the response time of the clipper beingused whereby the sheet material may be cut at a position remote from the operator at the exact location selected by the operator notwithstanding changes in the response characteristics of the clipper and any changes in the velocity of the sheet material.

It is another object of this invention to provide a photoelectric defect detecting means to sense the occurrence of a defect in moving sheet material such as wood veneer and to eliminate the drift in the reponse characteristics of the photocell, the intensity of the radiation source, or in the radiation transmission characteristics in what is considered acceptable material, and to establish in the photocell circuit a reference level of transmitted radiation through acceptable material immediately prior to the detection of a defective area within the moving sheet material to which the radiation passing through the defective region may be compared.

It is a further object of this invention to provide a means responsive to a defect signal from a photoelectric defect detecting element monitoring moving sheet material whereby a clipper located at a remote location may be caused to cut a defective portion a predetermined distance ahead of the defect and a predetermined distance behind the defect thereby to insure complete removal of the defective region.

It is another object of this invention to provide a detecting apparatus for monitoring moving sheet material and to separate acceptable portions of the material which exceed a predetermined minimum width from the remainder of the material.

It is a further object of this invention to provide a memory device to store cutting command signals which are too closely spaced in time for the proper operation of the mechanical cutting device, such a memory circuit reissuing the cutting signals after a sufficient time delay has elapsed to permit subsequent operation of the cutting device.

It is another object of this invention to provide a device which allows the constant observation of the edges of a sheet material for defects although the material may wander laterally within certain limits as it is being scanned by a photoelectric defect detecting device by simultaneously enabling and disabling pairs of photoelectric cells at opposite edges of the material.

These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings FIG. 1 is a simplified view of a defect detector constructed according to this invention showing the physical relationship of the defect detector with respect to the cutting means, and a simplified block diagram showing the electrical control circuitry;

FIG. 2 is a detailed sectional view of the radiation source, the wire forming the shadow line and the photocell defect detector;

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2 and shows a portion of the radiation source, shadow line, and photocell defect detector extending transversely across the sheet material;

FIG. 4 is a pictorial view of moving sheet material showing the relationship of the defect detector to th cutting means;

FIG. 5 is an electrical block diagram showing the electrical connections among the various electrical components which comprise the defect detector and clipper control circuits;

FIG. 6 is an electrical schematic of one of the photocell boards which comprise the photoelectric defect detector;

FIG. 7 is a schematic electrical diagram of the edge logic circuit which controls the photocells in use and allows the veneer ribbon to wander laterally;

FIG. 8 is an electrical schematic diagram of the logic circuit used when the photoelectric detector is operated in the round up fish tail mode;

FIG. 9 is an electrical schematic diagram of the automatic photocell threshold establishing circuit;

FIG. 10 is an electrical schematic diagram of the tachometer pulse amplifier and the standard length counter which supplies clipping pulses to the cutting means after a predetermined length of acceptable sheet material has passed through the cutting means;

FIGS. 11A and 11B are schematic electrical diagrams of the clip insertion and pulse holding circuit included in this invention;

FIG. 12 is an electric diagram of the main delay circuit with a portion of the circuit schematically shown in detail;

FIG. 13 is a schematic electrical diagram showing another portion of the main delay circuit; and

FIGS. 14A and 14B comprise a schematic electrical diagram of the clip delay servo circuit.

Referring now to the drawings which show a preferred embodiment of this invention, and particularly to FIG. 1 which is a simplified view showing the physical arrangement of the components which make up the defect detector and clipper control of this invention, a sheet of upgraded veneer 10 is moved by means of conveyor belts 11 between 100 and 200 feet per minute through a defect detector 12 and into a cutting means such as a clipper generally indicated at 13 where the defective region in the sheet may be isolated. The clipper 13 may also function to cut the sheet into standard lengths if no defects are observed.

The exact speed of sheet travel is measured by a tachometer 14 which provides an electrical pulse for each eighth inch increment of sheet travel. This tachometer pulse provides the necessary information required to cause the clipper subsequently to cut the moving sheet when a defective area is observed or when a predetermined length of veneer has passed through the clipper.

The machine operator is provided with a console 15 from which he may select the particular mode of operation for the machine. The operator may select by switch 16 the defect detecting mode wherein voids or knotholes in the veneer are detected and subsequently removed, or he may select the round up fish tail mode wherein acceptable wood exceeding a predetermined width may be isolated from unacceptable wood. The operator is also provided with a manual control 17 whereby he may initiate the operation of the clipper at any time. The operators console is also provided with a plurality of switch means 18 whereby he may activate the particular photocell region through which a defect will pass and simultaneously establish a reference level of the radiation transmitted through acceptable wood immediately prior to the defective area passing through the defect detector.

The operators console 15 is connected to a clip insertion circuit 20 which receives commands both from the manual operated switch 17 and from the photoelectric defect detector 12. The clip insertion circuit modities the output from the photocells and from the manually operated switch and applies this modified signal through a delay or memory circuit 21. The delay circuit 21, as well as the clip insertion circuit 20, are in part controlled in their operation by the output from the tachometer 14 and the output from the delay circuit 21. The output from the delay circuit 21 is applied to the clip delay servo circuit 22.

The function of the clip delay servo circuit 22, as will be described in detail later in this application, is to apply an electrical actuating signal to the clipper at such a time that the clipper knife will actually cut the veneer at the location selected by either the photoelectric defect detecting elements or by the operator observing the defect passing a reference line. In order to maintain accuracy in the cutting of veneer, a feed back signal 23 is generated when actual cutting of the veneer ribbon occurs and used to adjust the time of application of the electrical signal to the clipper such that the veneer ribbon is cut accurately at the preselected location notwithstanding variations in the respnse rate of the clipper.

The defect detector 12 is shown in detail in FIGS. 2 and 3 and includes a lamp assembly 25 comprising a bracket 26 supported above the moving sheet of veneer 10 by appropriate means, not shown. Secured to the bracket 26 is a plate 27 having downwardly sloping portions 28 which function as light shields. A plurality of lamps 30 are mounted in brackets 31 which in turn are secured to the plate 27 by insulators 32. A slot 33 in the brackets 31 receives the end of each lamp. Electrical current for supplying power to energize the lamps may be supplied to the bracket and then to the lamps through the bolt 34 which secures the lamp, bracket, and insulator to the plate 27. The lamps are designed to emit radiation primarily in the infrared region of the spectrum, although a portion of the radiation is visible. A sufficient number of lamps is provided to illuminate the entire width of the widest anticipated ribbon of ve neer.

, The defect detector 12 also includes a photocell as sembly 35 mounted on the opposite side of the veneer ribbon 10 and positioned to receive the radiation transmitted through the veneer. The photocell assembly 35 includes a plate 36 supported by suitable support posts 37 adjacent the underside of the moving veneer and the plate 36 in turn supports a bracket member 38 mounting the photocell boards 39 onto which the photocells 40 are secured. An aperture 41 is formed in the plate 36 and a glass plate 42 is mounted flush to the upper surface of the plate 36 to prevent dirt and wood particles from passing'through the aperture and accumulating on the photocells 40. It has been found that the glass will not lose its radiation transmission characteris tics even after being subjected to continuous rubbing by the veneer ribbon. Each photocell 40 has an adjusting potentiometer 43 associated therewith to provide the initial adjustment of the defect detector and insures an equal voltage output from each of the photocells 40 when the same intensity of radiation is applied thereto.

In the preferred embodiment of the invention described herein, a separate photocell 40 is provided to monitor each 1 inch width of the veneer. A plurality of shields 44 are secured to the plate 36 and are so positioned between the photocells that each photocell 40 senses only the radiation transmitted through the veneer for that area and does not sense the radiation transmitted through an adjacent area.

In the preferred embodiment, nine photocells monitor a nine inch width of the veneer and are connected electrically into what is termed a photocell area. These nine photocells are connected to a common amplifier means and therefore have a single electrical output which is a function of the maximum intensity of the light transmitted through the monitored 9 inch segment of veneer. Two photocell areas are connected electrically in parallel to form what is termed a photocell region which therefore monitors an 18 inch width of veneer. A total of seven photocell regions are used to monitor the entire width of the moving veneer ribbon.

The photocells used in the preferred embodiment of this invention were especially sensitive to infrared light. In view of the sensitivity of these cells to infrared, external sources of heat may adversely affect the sensitivity and operating levels of the photocells. Accordingly, means are provided to maintain the photocells at a near constant temperature by circulating conditioned air over the photocells and associated circuit components. This air is first cooled by a chilled water heat exchanger and then reheated to a regulated temperature by a fast acting electric heater controlled by a thermistor heat sensor. Therefore, with a constant temperature environment, the operating level of the photocells will not change and the cells will sense only the infrared energy which passes through the veneer ribbon.

The defect detecting assembly 12 further includes a shadow line forming means which includes a shadow line wire 45 placed to one side of the imaginary line which joins the lamp and the photocell. This wire 45 will cause a shadow to be formed on the moving ribbon of veneer at a location approximately one-half inch to one side of the center line of the aperture 41. By reference to this shadow line, the operator may visually observe a defect and manually control the operation of theclipper to accomplish accurate cutting of the veneer.

As shown in FIG. 4, the clipper 13 is a toggle type veneer clipper having a supporting member 47 mounted securely above the moving sheet of veneer 10. A knife blade 48 is secured to the member 47 by several toggles 49. A toggle bar 50 connects each of the toggles 49 and may be caused to move either to the'right or to the left by means of pistons slidably mounted in pneumatic cylinders 5i and 52, or by electric solenoids. In the embodiment shown, the toggle bar 50 is powered by a source of air pressure 53 supplied to the cylinder 51 at the left and to the cylinder 52 at the right hand side of the clipper, and electrically actuated set control valve 54 is provided to apply pneumatic pressure to alternate cylinders on command from the clip delay servo 22. As previously explained, the clipper 13 will have one of two different response times depending on whether the toggle bar is being moved to the right or to the left, thus giving the clipper an asymmetrical response characteristic. It is therefore important to apply the electrical actuating pulse at one of two different times in synchronism with the clipper operation in advance of the actual clipping location if accurate cutting of the veneer is to be accomplished.

The actual time when the knife 48 cuts the veneer is sensed by an impact detector 55 mounted on the supporting member 47. The output of this impact detector 55 is applied to amplifier 56, the output of which is a pulse of a standard width and amplitude. The output 23 of amplifier 56 is the feed back signal 23 used to adjust the time when the electrical actuating signal is applied to the clipper I3.

A block diagram of the connections among the various electrical components which comprise the veneer defect detector and clipper control circuit of this invention is shown in FIG. 5. The photoelectric defect detector 35 is divided into 14 areas designated 35a through 3511. A pair of photocell areas, such as areas 35a and 35b, comprise a region, and seven regions form the entire photocell assembly 35. It is anticipated that two different standard widths of sheet material may pass through the defect detector in the present invention, therefore, for the wider of the two widths, W1, nominally 125 inches, all of the photocell regions are utilized, but for the narrower of the two widths, W2, nominally 102 inches, the photocell region including areas 35b and 35n will be disconnected. A selector switch 58 is provided to select the width of sheet material to be monitored.

When monitoring a sheet having either awidth W1 or width W2, four of the photocells in either photocell area 351 or 35n as well as four photocells in area 35a do not continuously monitor the sheet but are provided with circuit means 60 to disconnect, for example, photocells in area 35a when a corresponding photocell in either area 351 or 3511 becomes covered by the edge of the sheet material thereby allowing the sheet to wander laterally without a signal indicating a defect being produced by the photocells at the edge of the sheet. The selector switch 58 determines whether the edge cell inhibit circuit will be connected to area 351 or to area 35n. Cable 61 carries the output of the photocells in each of these which have become covered and applies that information through the selector switch to the edge cell inhibit circuit 60. This circuit in turn supplies an inhibit signal along line 62 to the corresponding photocell at the opposite edge of the sheet.

The outputs from each of the regions comprising the photocell deflect detector 35 are applied along cable 64 to both the region defect threshold circuits 66 and the round up fish tail logic circuit 67. As previously explained, the apparatus described herein may be used either to detect and cut away a defect in a moving sheet of veneer or it may be used to isolate good veneer of a width exceeding a predetermined minimum width from the remainder of the veneer ribbon. The particular mode of operation may be selected by switch 16 on the operator's console 15. The outputs from both the region defect threshold circuit 66 and the round up fish tail logic circuit 67 are applied to the clip insertion logic circuit 20. In addition, the manually operated switch 17 is also connected to the clip insertion logic circuit 20 and may be used by the operator to produce a clipping signal when a defect is observed passing the shadow line reference.

The region defect threshold circuit 66 senses the voltage output from each of the photocell regions 35 and establishes a reference voltage corresponding to the intensity of the radiation transmitted through acceptable wood. When the operator observes a defect approaching the detector 12, he will close one of the switches 18 on the operators console 15 to select the photocell region through which the defect will pass, and when the selection is made, the region defect threshold circuit will be automatically calibrated, using the intensity of the radiation through the acceptable veneer immediately preceding the defect as a reference. In this way, frequent manual adjustments of the photocell sensitivity for various types of wood, thickness of veneer, etc., are eliminated.

The round up fish tail logic circuit 67 senses when a predetermined number of consecutive photocell regions sense the presence of acceptable veneer. In a preferred embodiment of the invention, the round up fish tail logic circuit 67 senses when three consecutive photocell regions observe a continuous width of acceptable veneer and the circuit 67 will product an output to cause the veneer ribbon to be cut thereby to isolate the acceptable veneer from the remainder of the ribbon when this mode of operation is selected by the operator.

As will be explained in detail hereafter, the output from the clip insertion logic circuit 20 is delayed by an amount determined in part by the mode of operation selected. For example, in the round up fish tail mode of operation the photocells sense the presence of an acceptable minimum width of wood and a clipping signal is applied to the clip insertion logic circuit 20. If the operator were to close switch 17 manually and apply a clipping signal to the circuit 20, it would be necessary to delay the ultimate clipping of the veneer by an amount equal to the displacement of the shadow line on the veneer. When the apparatus is used in the defect detecting mode, it is desirable to cause the veneer to be cut a small amount both before and after the defect signal is produced by the photocells to insure that the entire defective region is removed from the veneer ribbon. It has been found that a small amount of unacceptable veneer is associated with the defect as observed by the photocells.

A standard length counter 71 supplies an input to the clip insertion logic circuit 20 when either of two standard lengths of veneer pass beneath the defect detectors without a defect being observed. In a preferred embodiment of the invention, a clipping signal is applied to the clip insertion logic circuit 20 after the shorter standard length, nominally 27 inches,has moved under the defect detector since the last clipping signal and another signal is also applied after the veneer has moved under the defect detector for the longer standard length, nominally 54 inches. Since the longer of the two standard lengths is preferred, an inhibit signal will be applied along line 72 to inhibit the clipping signal for the shorter standard length.

The output from clip insertion logic circuit 20 is applied along line 73 to a selector switch 74 connected to the first stage main delay circuit 75. Further delay circuits 76 and 77 are also provided to delay the application of the clipping signal to the veneer clipper until the veneer has moved the distance from the defect detectorv to the clipper. The delay circuits 75, 76 and 77, as well as the clip insertion logic circuit 20 are controlled by pulses generated by the tachometer l4 and amplified by the tachometer pulse amplifier 78. These tachometer pulses are generated for every 95 inch increment of veneer travel. The amount of delay in delay circuit may be determined by the setting of switch 74 and is made adjustable in order to provide for flexibility in the installation of the defect detector and control circuit of this invention on presently existing veneer cutting equipment. The output from the main delay circuit 77 is then applied to the clip delay servo circuit 22.

The output from the clip delay servo circuit 22 is applied to the clipper control 54 at a time such that the knife will actually out the veneer after a standard time delay. The actual time of cutting of the veneer is detected by the impact detector 55, amplified by the amplifier 56 which produces a feed back pulse having a fixed predetermined amplitude and duration, and applies this pulse to the clip delay servo 22. The clip delay servo circuit 22 is actually two separate circuits which act alternately in synchronism with the clipper to compensate for the asymmetrical response characteristics of the clipper. The output from the clip delay servo to the clipper will, of course, vary in'time by an amount necessary to cause the knife to actually cut the veneer at the proper time.

PHOTOCELL CIRCUIT Referring now to FIG. 6, which is a schematic electrical diagram of one of the photocell areas which comprise the defect detector, with one of the nine photocell circuits comprising the area shown in detail. The photocells 40 are type T3SA20 Infratron photocells which are sensitive to the infrared radiation which is transmitted through the moving veneer sheet.

Each of the photocells in the area are provided with a positive bias voltage of between 6 and volts from a voltage divider network including potentiometer R1 and resistor R2. A capacitor C 1 functions to stabilize the bias voltage. A negative source of voltage is applied to the other side of the photocell through an individual adjustment potentiometer R3, and resistor R4. Diode CR1 prevents excessive voltage from being applied across the cell 40. Potentiometer R3 is so adjusted that the voltage output from each photocell circuit is the same when the same intensity of radiation is applied to the photocells.

The resistance of the photocell 40 will decrease as the intensity of the radiation falling on the cell increases, therefore, when more radiation falls on the cell, the voltage at the base of transistor 01 will increase and cause an increasing or positive going voltage at its emitter electrode.

The voltage at the junction of photocell 40 and resistor R4 may also be applied to the base of transistor Q2 provided that diode CR2 is biased into conductionby current flowing through resistors R3 and R4.

Transistor O2 is also connected to the other eight photocell circuits in the area and acts as a power amplifier supplying the output signal to the remainder of the system. The output from the emitter of transistor O2 is connected in parallel to the output from an adjacent photocell area which comprises the photocell region and the common output is directed throughcable 64 to either the region defect threshold circuit 66 or the round up fish tail logic circuit 67.

. For photocell areas 35a, 35! and 35n, four of the edge photocell circuits are provided with the individual output amplifier Q1. The output from the emitter of transistor O1 is applied along cable 61 to the edge cell inhibit circuit 60 and an inhibit signal may be applied along cable 62 to the junction between resistors R5 and R6. When it is desired to inhibit the output from a particular photocell in a photocell region due to the corresponding photocell at the opposite edge of the veneer ribbon being covered by the sheet, a ground potential will be applied on cable 62 and will place the junction between R5 and R6 at zero potential. This will cause diode CR2 to be biased into a non-conducting state and prohibits the voltage variations at the junction of photocell 40 and resistor R4 from being applied to the base of transistor Q2.

EDGE CELL INHIBIT CIRCUIT The edge cell inhibit circuit shown in FIG. 7 permits the veneer sheet to wander laterally and prevents a defect signal from the photocell at the edge which is uncovered from developing an output, provided that a corresponding-cell on the opposite edge of the veneer is covered by the veneer at the same time. A transistor is gated on when voltage from the individual output of the photocell at the edge of the veneer which is becoming uncovered develops a voltage of such magnitude to overcome a preset bias and causes another transistor to also be gated into the non-conducting state thereby to remove an inhibiting condition on the output of the corresponding photocell on the other edge of the sheet. Therefore, with the arrangement desired herein, the veneer sheet is permitted to move laterally within certain limits and while still monitoring the edge of the veneer sheet for defects.

The output from one of the photocells at one edge of the sheet, for example, one of the photocells in area 35a, is applied along cable 61 from transistor O1 to the base electrode of transistor Q3 through diodes CR4 and CR5. The collector electrode of transistor Q3 is grounded through resistors R7 and R8 when the edge cell circuits are enabled while the emitter electrode has a positive voltage supplied through transistor Q4. The voltage at the emitter of transistor O3 is determined by the setting of the adjustable tap on potentiometer R9 and establishes the threshold voltage above which the voltage on the base electrode of transistor Q3 must rise before that transistor will go into the non-conducting state. Since the edge cells are subjected to a wide range of change in the intensity of the radiation they receive, the edge cell threshold may be placed at a high level. Terminal 82 provides the same threshold voltage to several other similarly constructed circuits. In the present invention, eight circuits are connected in the manner described to allow the veneer sheet to wander through a total distance of 4 inches.

When the voltage on the base of transistor Q3 rises due to an increase in the intensity of the light falling on one of the photocells 40 in area 350, that transistor will cease conduction and cause the voltage applied on the base electrode of transistor O5 to decrease. The collector electrode of transistor O5 is connected by line 62 to the junction between resistors R5 and R6 (FIG. 6) in either the photocell area 311 or 35n, depending on the width of the veneer sheet being monitored, and when transistor Q5 ceases to conduct, current is allowed to pass through resistor R6 to bias diode CR2 into the conducting state and allow the variations in voltage from photocell 40 to be applied to the base of transistor 02. At this time, therefore, when the photocell on one edge of the veneer becomes uncovered, the corresponding photocell on the other side will be placed into operation and defect detection will continue as previously explained.

ROUND UP FISH TAIL CIRCUIT When the operator adjusts switch 16 on the operators console to select the round up fish tail mode of operation, the circuit 67 shown in FIG. 8 is placed into operation. This circuit is connected directly to the output from the photocell areas and senses when veneer of acceptable quality having a width which exceeds three photocell regions is present beneath the detector. When this condition occurs, an output signal from this circuit is developed which is applied to the clip insertion circuit 20 and which ultimately causes the veneer to be cut and separate the acceptable portion from the unacceptable portion. The circuit 67 also senses when the acceptable portion of the veneer having the predetermined minimum width moves laterally and acceptable veneer is no longer present under any one or more of the three photocell regions which initially sensed the acceptable width of veneer even though three other consecutive photocell regions subsequently provide an output indicating acceptable veneer.

In the circuit shown in FIG. 8, the output from each of the photocell regions is applied along cable 64 to a set of five NOR gates, each formed from a combination of three isolating diodes and a transistor. Thus, the three photocell regions comprising photocell areas 35a and 35b, 35c and 35d, and 35s and 35f are connected to the first NOR gate comprising transistor Q6 by lines 83, 84 and 85, respectively. Therefore, each of transistors 06 through Q10 are connected to three consecutive photocell regions through lines 83 through 89 which form the cable 64. The transistors of the AND gates are connected to these lines through isolating diodes which serve to prevent a signal from one area from appearing on a line carrying a signal from another area. Each of these AND gates is enabled when the three consecutive photocell regions connected thereto develop an output representing the occurrence of acceptable veneer.

The collector electrodes of transistors Q6 through Q10 are connected through resistors R11 through R to the base electrodes of transistors Q11 through Q15. The emitter electrodes of transistors Q11 through Q15 are connected to a positive source of voltage, while the collector electrodes are connected to lines 91 through 95, respectively. Each of these lines is connected through a collector load resistor to a suitable source of negative voltage. Each of lines 91 through 95 is also connected to the base electrode of all the other transistors Q1 1 through Q15 through an isolating diode. Thus, the collector of transistor Q11 is connected to the base electrode of each of transistors Q12 through Q15 through an isolating diode but not to its own base electrode. Therefore, the operation of one transistor may control the operation of all of the other transistors connected to it.

Each of the lines 91 through 95 is also connected through another set of isolating diodes to the base electrode of transistor Q16 which forms a part of the output circuit. The collector electrode of transistor Q16 is connected directly to the base of transistor 017, the collector electrode of which is connected to the clip insertion circuit by line 97 and to the base electrode of transistor Q18. The collector electrode transistor Q18 is connected to the clip insertion circuit 20 by line 98. Transistor Q17 provides an output to the clip insertion circuit causing a cutting signal to be developed when the veneer exceeds a predetermined minimum width while transistor Q18 supplies the signal to the clip insertion circuit when the veneer width decreases below the minimum width or when the acceptable width of veneer moves from one set of photocell regions to another set.

The bias voltage for transistors Q6 through Q10 is supplied on line 100 from the junction of the emitter electrode of transistor Q19 and resistor R16. The magnitude of the voltage on line 100 is determined by the setting of the adjustable tap on potentiometer R17 and establishes the value of the voltage which must be applied to the base electrodes of transistors Q6 through Q10 to cause them to go into the non-conducting state.

Before the veneer sheet begins to pass between the radiation source and the photocell detectors, a maximum intensity of radiation is falling on the photocells in each region and causes the maximum possible positive voltage output to be present on lines 83 through 89. Under these conditions, each of transistors Q6 through Q10 will be gated on or into the conducting state. As acceptable wood begins to move between the radiation source and the detectors, the voltage level on certain of lines 83 through 89 will decrease and when the voltage level on three consecutive lines indicates the presence of acceptable wood, for example on lines 83 through 85, the transistors Q6 will be gated into a non-conducting state and cause a rie in the voltage level on the base of transistor Q11 to gate that semiconductor into the non-conducting state also.

When transistor Q11 ceases conducting, the voltage on line 91 will change from a positive value to a negative value of such a magnitude that the voltage applied to the base electrode of transistors Q12 through Q15 will cause these elements to remain in the conducting state nothwithstanding any subsequent changes in the state of conduction of transistors Q7 through Q10.

The change in voltage on line 91 will also be reflected onto the base electrode of transistor Q16 through the isolating diode to cause that semiconductor to cut off and thereby gate transistor Q17 to conduction. At this time, a negative going signal from the collector transistor Q17 will be applied to the clip insertion circuit 20 along line 97 to cause the dvelopment of a clipping signal. Also, the base of transistor Q18 will become less positive to cause that element to gate off and apply a positive going signal on line 98 to the clip insertion circuit. However, only negative goingsignals are utilized by the clip insertion circiut 20 to develop the necessary pulse to cause the clipping of the veneer.

When the width of the veneer sheet becomes less than the three regions including photocell areas 35a through 35f, the voltage level on one or more of lines 83 through 85 will increase and transistor Q6 will again conduct and cause transistor Q11 to be gated on thus raising the voltage on line 91 and removing the biasing voltage on the base electrodes of transistors Q12 through Q15. Transistor Q16 resumes conducting and a negative going voltage will appear at the collector electrode of transistor Q18 which will be applied on line 98 to the clip insertion circuit 20.

Assuming, for example, that in addition to photocell areas 35a through 35f sensing acceptable veneer, the photocell areas 35g and 35h also begin to sense acceptable veneer. This condition will cause a lower voltage to be developed on line 86 as well as on lines 83 through 85 and will cause transistor O7 to go into the non-conducting state. The voltage at the base of transistor Q12, however, will not change due to the voltage applied thereto from line 91 due to the action of transistor Q11. Therefore, the covering of an additional photocell region with acceptable veneer will have no apparent effect on the remainder of the circuit. 

1. A process for detecting and separting acceptable sheet material exceeding a predetermined minimum width from moving sheet material comprising the steps of: directing a source of radiation toward said sheet material; sensing the intensity of the radiation passing through said sheet material by a plurality of photoelectric cells; establishing when a predetermined number of consecutive photocells sense the presence of acceptable sheet material to produce a first electrical signal; producing a second electrical signal when the width of the acceptable sheet material in said moving ribbon decreases below said predetermined width or when the predetermined number of consecutive photocells sensing acceptable sheet material changes and does not include the same photocells initially sensing the minimum width of acceptable sheet material; utilizing said first and second signals to actuate a cutting device thereby to separate acceptable sheet material of at least a predetermined width from acceptable sheet material and from sheet material of acceptable width which does not have at least one edge portion corresponding to an edge of the sheet material initially having the minimum predetermined width.
 2. A process for detecting and removing defects from moving sheet material, comprising the steps of: directing a source of radiation toward said sheet material; sensing the intensity of the radiation passing through said sheet material by a plurality of photoelectric cells; producing a reference signal indicating the level of radiation passing through acceptable material; producing an electrical signal indicating the occurence of the defect when the intensity of the radiation transmitted through said sheet material increases above said reference level; and utilizing said electrical signal to cut the sheet material at a location remote from said photocells after the sheet material has moved a predetermined distance.
 3. A process for detecting and removing defects from moving sheets of wood veneer comprising the steps of directing a source of radiation toward said veneer, sensing the radiation passing through the veneer by a plurality of photodetectors, producing cutting command signals when the radiation passing through the veneer exceeds a predetermined amount, cutting the veneer to remove the defects at a location downstream of the photodetectors by a toggle action veneer clipper having two actuation response times, delaying the application of said cutting command signals to said clipper until the veneer moves from the photodetectors to the veneer clipper, determining the two actuation response times of the clipper, and adjusting the time delay of the application of the cutting command signals to the clipper such that the sheet material is cut at a location preselected by the photodetectors to remove defects independently of the actuation response time of the clipper.
 4. The process of claim 3 further including the steps of sensing the leading and trailing edges of defects in wood veneer and modifying the application of the cutting command signals to the clipper in such a way that the veneer is cut a predetermined distance prior to the defects and predetermined distance after the defects. 